Lightning arrester with pressure relief means

ABSTRACT

A lightning arrester with means for relieving internal pressure by venting the housing in case of failure of the arrester. The housing is closed at the end by a thin sealing plate and a piercing member is disposed inside the housing adjacent the plate. An explosive disconnector device is provided on the outside of the housing, and in case of failure of the arrester the disconnector operates and drives the plate onto the piercing member to puncture the plate and relieve internal pressure in the housing.

United States Patent 1151 3,702,419 Carothers et al. 1 Nov. 7, 1972 54] LIGHTNING ARRESTER WITH 3,100,246 8/1963 Riley ..3l7/66 PRESSURE RELIEF MEANS Primary Examiner-J. D. Miller [72] Inventors g s gs ig s zb g gg fi Assistant Examiner-Harvey Fendelman 03 e o g Attorney-A. T. Stratton [73] Assignee: Westinghouse Electric Corporation, v

, Pittsburgh, Pa. 7 [57] ABSTRACT [22] Filed: Sept. 28, 1971 A lightning arrester with means for relieving internal pressure by venting the housing in case of failure of [21] Appl' l8447l the arrester. The housing is closed at the end by a thin sealing plate and a piercing member is disposed inside [52] US. Cl. ..317/61, 317/71, 337/30, thehousing adjacent the plate. An explosive discon- 317/66 nector device is provided on the outside of the hous- [51] Int. Cl. ..H02h 1/04, H0211 9/06 ing, and in case of failure of the arrester the discon- [58] Field of Search ..317/62, 66, 70, 71, 72; nector operates and drives the plate onto the piercing 337/19, 28, 30, 34; 315/35, 36; 3l3/DIG. 5 member to puncture the plate and relieve internal pressure in the housing. 1 1 [56] Reerences Cited I 9 Claims, 3 Dravving Figures UNITED STATES PATENTS 3,144,583 8/1964 Sorrow ..315/36 I 31 LIGHTNING ARRESTER WITH PRESSURE RELIEF r MEANS BACKGROUND OF THE INVENTION Thepresent invention relates tolightning arresters, and more particularly to distribution arresters provided with an external disconnector means or dropout device. I

' Modern distribution lightning arresters are highly reliable devices, but occasional failures may occur if an arrester is subjected to voltages above its rating or to surge currents beyondits capacity or under other abnormal conditions. Although such failures are rare, I

when a failure does occur, the arrester cannot interrupt the power current flowing through it after. a surge has been discharged, and the continuous current thus flowing will reach a magnitude equal to the maximum short- N circuit current available at the point onthe system 'to which the arrester is connected. The failure therefore results in grounding the system, and the heavy current flowing in the arrester causes an extremely rapid buildup of gas pressure in the sealed arrester housing due to vaporization of the arrester valve block material. Ar-

Failure of an arrester therefore involves the risk of dan-.

gerously highinternal gas pressures which may cause shattering or explosion of the porcelain housing with 1 resulting danger to persons who maybe in the vicinity and risk of damage to adjacent "equipment or other nearby property.

Various means of relieving the'internal gas' pressure upon failure of a lightning arrester have been proposed. Thus, the disconnector device may be designed so that an external arc produced by interruption of the arrester current burns a hole through asealing plate at the bottom of the arrester to permit the gas to escape, as disclosed in our prior U.S. Pat. No. 3,291,937. This arrangement, however, has certain disadvantages such as the inherent-time delay in starting the pressure relief, as the hole is not burned in the plate until after the disconnector has operated and an arc has formed. Since the arc is on the outside of the arrester, it is subject to atmospheric conditions and the arc terminalmay move away from the sealing plate due to wind or other external conditions. Thus, this means of pressure relief is not entirely satisfactory. Sealing plates or diaphragms'have been designed to rupture in response to deformation of the plate caused by the internal gas pressure in the housing. This, however, is a relatively slow and unreliable expedient and it has also been proposed to make rupture of the plate faster or more certain by placing external puncturing means adjacent theplate, as in the U.S. Pat. to Kalb et'al. No. 2,915,674 and Schultz No. 2,928,016, or by placing shearing members in contact with the plate so as to insure positive opening of the plate in response to internal pressure as in our copending patent application Ser. No. 59,177, filed July 29,

1970 now U.S. Pat. No. 3,644,791, and assigned to the assignee of the present invention.

SUMMARY OF THE INVENTION 1 In accordance with the present invention, there is provided a distribution lightning arrester which provides substantially instantaneous pressure relief in case of failure in an inexpensive and highly reliable manner. The bottom of the arrester housing is closed and sealed by a relatively thin sealing plate or diaphragm and a disconnector device, preferably of the explosive type, is attached to the outside of the housing enclosing the sealing plate. A piercing member having a cutting point is supported on the inside of the housing closely adjacent to the sealing plate. Upon failure of the arrester,

. the disconnector operates in the usual manner to blow off the ground lead and at the same time drives the sea]- ing plate onto the internal piercing member to puncture a hole in the plate and thus ventthe housing to relieve the internal pressure. In this way a simple but fast and highly reliable pressure relief means is provided.

" BRIEF DESCRIPTION OF THE DRAWING DESCRIPTION OF PREFERRED EMBODIMENT The invention is shown in FIG. 1 embodied in a distribution'lightning arrester which may be of any usual or suitable type. As shown, the arresterhas a porcelain housing 10 ,of usual construction which is closed and sealedat the top by a top cap member 1 1 of any desired type which supports aterminal stud 12 or other terminal means for connection of a line lead. The arrester may be of any desired internal construction and plate utilpreferably consists of the usual series arrangement of spark gaps and valve blocks or non-linear resistors disposed in a column in the housing 10. The internal arrester elements have not been shown in detail as they are not a part of the invention and they are disposed in a column in the housing 10, the lowermost valve block 13 being visible in FIG. 1.

The arrester is provided with a disconnector device generally designated 14 at the lower end. Any suitable type of disconnector device, preferably of the explosive type, may be utilized, and the particular disconnector shown in the drawing for the purpose of illustration is of the type more fully disclosed and claimed in a copending application of C. H. Carothers et al., Ser.

No. 76,573, filed Sept. 29,- 1970, and assigned to the assignee of the present invention. i

As more fully described in that application, the disconnector 14 has'a generally cup-shaped housing 15 of any suitable plastic or other insulating material which is frangible so as to be easily ruptured in response to internal force. The housing 15 supports a ground terminalstud 16 which has a flat head 17 within the housing supported on its bottom inner surface. The terminal stud 16 is sealed byan O-ring 18 or other suitable seal and is secured to the housing 15 by a nut 19. Within the housing 15. there is disposed a body member 20 molded of insulating material and supporting an explosive cartridge 21 which rests in a recess in the head 17 of the terminal stud 16 so as to be in electrical contact with the terminal stud. A compression spring 22 and current-carrying shunt 23 are attached to the top of the body 20 by a rivet 24 the head of which is positioned in a recess within the body 20 and spaced from the explosive cartridge 21 so as to form a spark gap therewith. A resistor 25 of any suitable type is positioned at the side of the body 20 and is connected to the rivet 24 by a contact strap 26 and to the head of the explosive cartridge 21 by a contact strap 27.

The lower end of the arrester housing 10 is closed and sealed to prevent entrance of moisture into the arrester. For this purpose the disconnector 14 is attached to the bottom of the housing 10 by a metal flange 28 which is rolled or spun over the lower end of the housing 10 and over a flange portion of the disconnector housing 15, as shown in FIG. 1, to securely attach them together, a gasket 29 being utilized to seal the joint between the disconnector and the arresterhousing. The open bottom of the housing 10 is closed and sealed by a sealing plate 30. The plate 30 is a thin metal plate of aluminum orother suitable material such as copper, which is thin enough to be frangible so as to be easily ruptured, and which may be provided with stiffening ribs 31 embossed in the plate as shown inFlG. 3. The plate 30 is placed on top of the disconnector housing 15 as shown in FIG. 1, engaging the spring 22, and extends between the disconnector and the gasket 29 to seal the housing. The plate 30 is further sealed by an O- ring seal 32 between the plate 30 and the disconnector housing. The bottom of the arrester is thus effectively closed and sealed by the plate 30, and the disconnector l4 encloses and protects the thin and relatively fragile plate 30 in normal operation.

A support plate 33 is, provided in the bottom of the arrester housing 10 to support the internal arrester elements. The plate 33 is shown in FIG. 2 and may be made of steel or other suitable conducting material. The plate 33 is made sufficiently heavy to have enough mechanical strength to support the arrester elements, and is of the configuration shown in FIG. 2 with rounded ends 34 which fit within the gasket 29 and with straight sides so that there is ample space on each side of the plate 33 for gases to escape from the interior of the arrester. The ends 34 are rounded to conform to the shape of the gasket 29 and are offset from the plane of the plate 33, as seen in FIG. 2, so as to rest on the plate 30 near its periphery while the central part of the support plate is spaced from the sealing plate 30. At the center of the plate 33 a portion 35 is lanced downward. The lanced portion 35 has a triangular end so that when bent downward as shown it forms a sharp piercing point which is disposed closely adjacent the center of the sealing plate 30 as can be seen in FIG. 1. The portion 35 may of course have any desired configuration to provide a cutting or piercing point or edge adjacent the plate 30. The support plate 33 thus rests at its ends 34 on the plate 30 near its periphery and is supported by the housing 15 of the disconnector, so that the thin plate or diaphragm 30 is not subjected to any great stress under normal conditions as the weight of the internal arrester elements is carried by the plate 33 and the disconnector housing 15. Y

The arrester is connected between line and ground by means of the line terminal 12 and the ground stud 16, the electrical circuit extending through the arrester elements from the terminal 12 to the steel support plate 33, the metal sealing plate 30 and to the spring 22 and shunt 23 which form the terminal of the disconnector 14. As more fully explained in'the above-mentioned copending application, the disconnector 14 provides two parallel paths, one of which extends from the spring 22' through the rivet 24 and across the spark gap to the explosive cartridge 21 and to the ground terminal 16. The other path extends from thespring 22 through the resistor 25 to the ground terminal in parallel with the path across the spark gap.

Under normal conditions, any small leakage current through the arrester is carried by the current path through the resistor. When the arrester operates to discharge a surge, an extremely high current may flow and causes the gap between the rivet 24 and cartridge 21 to are over. If the arrester operates normally, the current is interrupted within a half-cycle and the disconnector 14 does not operate. However, if the arrester fails for any reason to interrupt the current flowing through it after a surge has been discharged, and the current continues to flow, the gap in the disconnector continues to are and the explosive cartridge 21 will be very quickly heated sufficiently to cause it to detonate. When the explosive 21 detonates, the frangible housing 15 of the disconnector isimmediately ruptured andfalls apart, so that the lower part of the housing carrying the ground terminal 16 and the attached ground lead falls or is blown off.

At the same time the explosive force due to the detonation of the cartridge 21 produces a high impact force upon the thin sealing plate 30 which closes the upper end of the disconnector housing. The plate 30 is also a frangible member and is driven upward with considerable force by the impact of the explosion and is driven onto the point of the lanced piercer member 35 of the support plate 33. The plate 30 is thus pierced or punctured by the point 35 to open the arrester housing and vent the gas therein to relieve the pressure. It will be understood that as soon as the disconnector has operated, the bottom part of the housing 15 falls away leaving the bottom of the arrester open to atmospheric pressure. The higher internal gas pressure in the arrester housing therefore tends to force the plate 30 downward off the piercer point 35 immediately after the explosion impact force has been dissipated. The gas can thus escape through the pierced hole in the plate 30 with little or no obstruction. The internal gas pres sure is quickly relieved in thisway and the danger of shattering the porcelain housing is eliminated. The upper part of the disconnector housing 15 remains attached to the arrester housing by the flange 28 so that the support plate 33 remains in its normal position. The internal arrester elements therefore are still supported on plate 33 and are prevented from falling out of the' housing after operation of the disconnector.

It will now be apparent that the new lightning arrester structure provides for substantially instantaneous venting of the arrester housing upon failure of the arrester, so that internal gas pressure is efi'ectively relieved and dangerous gas pressures are prevented. This result is obtained in a simple and inexpensive manner but the operation is highly reliable. The venting occurs immediately upon operation of the disconnector, so that it is substantially instantaneous, and does not dependon formation of an external arc or on deformation of a diaphragm after the internal gas pressure has built up.

We claim:

1. A lightning arrester having a housing containing arrester elements, sealing means at one end of the housing including a frangible portion, a piercing member inside the housing positioned closely adjacent said frangible portion of the sealing means, and disconnector means attached to the outside of the housing adjacent said frangible portion, said disconnector means being responsive to failure of the arrester to interrupt current therethrough and being operative upon such failure to effect disconnection of the arrester and to drive said frangible portion onto said piercing member to pierced thereby.

2. A lightning arrester as defined in claim 1 in which the frangible portion of the sealing means is a thin metal plate closing one end of the housing.

3. A lightning arrester as defined in claim 1 in which the disconnector means includes an explosive element.

4. A lightning arrester as defined in claim 1 in which the frangible portion of the sealing means is a thin metal plate closing one end of the housing and the disconnector means includes a housing enclosing said metal plate and containing an explosive element.

5. A lightning arrester having a housing containing arrester elements, sealing means at one end of the housing including a thin metal plate closing the housing, a support member within the housing adjacent said plate and adapted to support the arrester elements, a piercing member on the support member closely adjacent to said plate, disconnector means attached to the housing adjacent the outside of said plate, said disconnector means being responsive to failure of the arrester and being operative in case of failure to effect disconnection of the arrester and to drive said plate onto said piercing member to be pierced thereby.

6. A lightning arrester as defined in claim 5 in which said piercing memberis a bent out portion of the support member having a pointed end closely adjacent the metal plate. A

7. A lightning arrester as defined in claim 5 in which said disconnector means includes an explosive element.

8. A lightningarrester as defined in claim 5 in which said disconnector means includes a frangible housing attached to the arrester housing and enclosing said metal plate, said frangible housing supporting a terininal member and being adapted to be ruptured upon operation of the disconnector means.

9. A lightning arrester as defined in claim 8 in which said piercing member is a bent out portion of the support member having a pointed end closely adjacent the metal plate, and said frangible housing contains an explosive element to effect operation of the disconnector means. 

1. A lightning arrester having a housing containing arrester elements, sealing means at one end of the housing including a frangible portion, a piercing member inside the housing positioned closely adjacent said frangible portion of the sealing means, and disconnector means attached to the outside of the housing adjacent said frangible portion, said disconnector means being responsive to failure of the arrester to interrupt current therethrough and being operative upon such failure to effect disconnection of the arrester and to drive said frangible portion onto said piercing member to pierced thereby.
 2. A lightning arrester as defined in claim 1 in which the frangible portion of the sealing means is a thin metal plate closing one end of the housing.
 3. A lightning arrester as defined in claim 1 in which the disconnector means includes an explosive element.
 4. A lightning arrester as defined in claim 1 in which the frangible portion of the sealing means is a thin metal plate closing one end of the housing and the disconnector means includes a housing enclosing said metal plate and containing an explosive element.
 5. A lightning arrester having a housing containing arrester elements, sealing means at one end of the housing including a thin metal plate closing the housing, a support member within the housing adjacent said plate and adapted to support the arrester elements, a piercing member on the support member closely adjacent to said plate, disconnector means attached to the housing adjacent the outside of said plate, said disconnector means being responsive to failure of the arrester and being operative in case of failure to effect disconnection of the arrester and to drive said plate onto said piercing member to be pierced thereby.
 6. A lightning arrester as defined in claim 5 in which said piercing member is a bent out portion of the support member having a pointed end closely adjacent the metal plate.
 7. A lightning arrester as defined in claim 5 in which said disconnector means includes an explosive element.
 8. A lightning arrester as defined in claim 5 in which said disconnector means includes a frangible housing attached to the arrester housing and enclosing said metal plate, said frangible housing supporting a terminal member and being adapted to be ruptured upon operation of the disconnector means.
 9. A lightning arrester as defined in claim 8 in which said piercing member is a bent out portion of the support member having a pointed end closely adjacent the metal plate, and said frangible housing contains an explosive element to effect operation of the disconnector means. 